Fail safe electromagnetically operated brake devices have been found to be particularly desirable in applications where an electrical power failure is a possibility. In those applications it is desirable, upon the loss of electrical power, to engage the brake in order to bring a device to a complete standstill condition and to maintain the standstill condition until power has been restored. For example, in an electric lift truck, it would be desirable, in the case of an electrical system failure, to stop the forks in the position that they attained prior to the electrical failure. This would insure that the lift, with its heavy load, would not drop to the floor and cause serious damage. Also, in a lift truck, the fail safe electromagnetic brake can be used when the engine stalls so that the truck would come to a complete standstill condition upon power failure.
Other uses of this type of device are in an elevator where it would be necessary to stop the elevator in case of a power failure. Thus, in general, the fail safe electromagnetic brake is used in any application where it is desired, in case of a loss of electrical power, to stop functioning of certain electrical components to avoid a major breakdown or disaster.
Such applications place particular requirements on the brake device in that, generally, the brake device must be simple and economically constructed and at the same time provide positive engagement under a high torque absorption in order to enable the mechanical system in which the brake is utilized to safely avoid continuation of the event cycle. A break in such a system may be either off or on for long periods of time or cycled on and off for short periods of time depending on the application requirements. Thus, the brake must be sufficiently durable to withstand constant use with a minimum amount of wear.